Known fill-level measuring devices for contactless measuring comprise an antenna that emits and receives signals (radar signals, microwaves or ultrasound) in order to determine the fill level of a medium, e.g. in a product container. In such a setup the antenna of such a fill-level measuring device is, for example, arranged within the container.
In this arrangement the quality of the measuring signals received during fill level measuring with the use of a fill-level measuring device strongly depends on the quality of the transmitting/receiving unit. In particular, in this arrangement the strength or amplitude of the receiving signal is critical. If the amplitude is low, for example because the measuring signal has been considerably attenuated on its path from the transmitter to the product and back, or if the product provides poor reflection, the quality of signal evaluation and thus the measuring result suffer. In contrast to this, if the amplitude of the received signal is excessive, the receiving unit often overdrives. This subsequently results in incorrect measuring.
From DE 10 2005 057 094 A1 it is known to vary the transmission power for measuring a fill level in that switching occurs between two different oscillators, in other words between two different sources for generating transmitting signals which in each case comprise different transmission powers.